Transfer kinetics of phosphorus (P) in macrophyte rhizosphere and phytoremoval performance for lake sediments using DGT technique

Abstract

DGT (diffusive gradients in thin films) technique and DIFS (DGT induced fluxes in sediment) model are firstly designed for macrophyte-rhizobox system and in-situ macrophytes in Lake Erhai. Dynamics of phosphorus (P) transfer in Zizania latifolia (ZL) and Myriophyllum verticiilatur (MV) rhizosphere is revealed and phytoremediation performance for P in sediment is evaluated. Dynamic transfer process of P at DGT/sediment interface includes (i) diffusion flux and concentration gradients at DGT(root)/porewater interface leading to porewater concentration (C0) depletion and (ii) P desorption from labile P pool in sediment solid to resupply C0 depletion. Fe-redox controlled P release from Fe-bound P (BD-P2) and then NH4Cl-P1 in rhizosphere sediment resupplies porewater depletion due to DGT (root) sink. Kd (labile P pool size in solid phase), r (resupply ratio) and kinetic exchange (Tc and k-1) lead to change characters of DIFS curves of (1) r against deployment time and (2) Csolu (dissolved concentration) against distance at 24 h. They include two opposite types of “fast” and “slow” rate of resupplies. Sediment properties and DIFS parameters control P diffusion and resupply in rhizosphere sediment. Phytoremoval ability for sediment P in lake is estimated to be 23.4 (ZL) or 15.0 t a−1 (MV) by “DGT-flux” method.